Ning Liu

The as-cast Al ₁₅ Co ₂₀ Cr ₂₅ Fe ₂₀ Ni ₂₀ high-entropy alloy consisted of FCC and BCC, including an ordered NiAl-type B2 phase. After annealing at 500, 600, and 1000°C, the A5, A6, and A10 samples show excellent phase stability. Conversely, the σ phase emerged after annealing at 700, 800, and 900°C. Moreover, the influence of temperature on the phase stability is stronger than that of holding time. The experimental results agree with the calculated phase diagram at high temperatures. The A7–A9 samples exhibit excellent wear resistance for the formation of the σ phase. Additionally, the Al ₁₅ Co ₂₀ Cr ₂₅ Fe ₂₀ Ni ₂₀ samples at various states display different wear mechanisms.

The effects of elements In, Bi and Sb with 1, 2, 3, 4 and 5 wt% added to pure Sn metal were investigated, in order to study their influence on their melting behavior, microstructure and mechanical properties. The findings indicate that the addition of In, Bi and Sb reduces the undercooling of pure Sn. After adding the three elements to the Sn/Cu solder joints, the microstructure remains predominantly composed of the β-Sn phase and the Cu₆Sn₅ phase, aligning with the microstructures of the corresponding Sn based bulk alloys. The difference arises when Bi is added up to 5 wt%, leading to the precipitation of Bi particles. The element In, however, only dissolves in the β-Sn and Cu₆Sn₅ phases. When the mass fraction of Sb reaches 5%, a dark gray square SbSn phase precipitates. Among the elements, Bi and In play the role of solid solution strengthening, due to the precipitation phase of Bi and the presence of SbSn phase. Additionally, Bi and Sb exhibit precipitation strengthening effect. These strengthening effects make the maximum shear force and microhardness of the joints with the increase in the amount of alloying elements added to show a monotonous upward trend. The results show that the strengthening effect of Bi is superior to that of Sb,In when the doping amount of alloying elements is the same. The research results have guiding significance for alloy design, especially in the field where the reliability of electronic equipment is required at high temperature.

Laser-cladding CoCrFeMoNi high-entropy alloy coating is composed of face-centred cubic, σ and µ phases. After annealing at 700 °C, many needle-like precipitates of the σ phase are found in the FCC solid solution, and the granular µ phase precipitated at the edge of the primary net-structural σ phase. After annealing at 800 °C, granular µ phases are found inside the primary σ phase. The friction coefficients of the coatings (as-cladded, as-annealed at 700 °C and 800 °C) decrease dramatically compared with the substrate of H13 steel. Obvious spheroidising of the σ phase at 900 °C leads to a decrease of hardness and an increase of friction coefficient. Furthermore, the CoCrFeMoNi high-entropy coatings show better corrosion resistance than H13 steel in 3.5 wt-% NaCl solution.

In this work (CoCrNi)_100−x Nb _x (x = 0–23.08 at.%) medium-entropy alloys were designed to investigate the solidification process and principle. The solid solubility of Nb in CoCrNi equiatomic MEA was discovered to be less than 0.46 at.%, and a fully eutectic structure was obtained at Co_28.9Cr_28.9Ni_28.9Nb_13.3 alloy. Fcc and Laves phases are the main component phases in the (CoCrNi)_100−x Nb _x alloys. With the increasing Nb content, the volume fraction of fcc decreased, accompanied by the increment of Laves phase. Based on CALPHAD and experimental results, the top-left corner of the (CoCrNi)Nb pseudo binary phase diagram was achieved. Hypoeutectic (CoCrNi)_100−x Nb _x (x < 13.3 at.%) alloys undergo the following solidification process: at first, primary dendrites with fcc structure nucleate and grow in the melt, then, eutectic reaction occurs and a mixture of Laves and fcc eutectic structure is obtained. Conversely, for hypereutectic (CoCrNi)_100−x Nb _x (x > 13.3 at.%) alloys, the primary dendrite of Laves phase form, followed by the eutectic reaction of L → fcc + Laves.